The present invention relates to chair controls and more specifically body weight chair controls in which the major force employed to return the chair to, and support the chair in, its upright or task position are supplied by the user's weight within the chair.
The present invention also relates to synchrotilt chair controls wherein the chair back and the chair seat both tilt, but at different rates, to maintain a comfortable dynamic interrelationship between the seat and back.
In contrast, most common types of chair controls include a control attached only to the chair seat such that the chair and back tilt at the same rate or a control attached only to the back such that the back tilts but the seat does not. In these controls, some type of relatively strong biasing means is necessary to return the occupied chair to its upright or task position. However, when the occupant of the chair increases the biasing force to obtain the desired task position support, the biasing force is too great to allow the occupant to remain comfortably in the reclined position. Conversely, if the occupant adjusts the control to decrease the biasing force to enable him to comfortably recline the chair, inadequate task support is provided.
Body weight chair controls typically require complex linkages for distributing the forces in the chair control so that the force exerted against the back of the chair when one tilts backwards is at least partially offset by the occupant's body weight upon the chair seat. Prior body weight controls typically provide linkage in the chair control between the back support and the seat support to push the seat forwardly and upwardly as the chair back is reclined. Examples of such structure are shown in U.S. Pat. Nos. 2,796,918 issued June 25, 1957 to Luckhardt, 2,760,556 issued Aug. 28, 1956 to Henrikson et al, and 2,612,211 issued Sept. 30, 1952 to Gielow et al. A serious problem with this arrangement is that the user has the feeling as he leans back that the chair back and seat are separating from one another due to the shift between the seat and the chair back as the chair is reclined and the seat is pushed forward. This action can cause some discomfort as the user's clothes are pulled in opposite directions.
Another prior approach is to pivot the chair seat and back precisely over the chair's center of gravity. Therefore, a slight shift of weight by the occupant will result in movement of the chair control. This construction is shown in U.S. Pat. No. 2,615,496 issued Oct. 28, 1952 to Lorenz et al. Because the center of gravity is so critically located, this chair does not provide the desired task support necessary for many functions such as typing and key punching. Furthermore, the chair seat tilts excessively as the chair reclines thereby tending to raise the user's feet off the floor.